A plenty of techniques for effectively operating an electric power supply system using a DC generator and system power have been developed.
For example, Patent Document 1 shows an electric power supply system for feeding electric power to a load through an electronic transformer commonly operated at operation efficiency of almost 100% by combining natural energy power and nighttime power. More particularly, the rated power voltage of a wind power generator, a photovoltaic generator and a fuel cell is coincident with the rated voltage of a storage battery to construct a DC power source. Until the storage battery is fully charged by the DC power source, AC power is supplied to the load from a commercial AC power source. When the storage battery is fully charged or the commercial AC power source is in a power failure, DC power is supplied from the DC power source and the storage battery. While the storage battery is discharging electric power, power energy is complemented from the fuel cell. During the time of the daylight power supply or the nighttime power supply, AC power is supplied to the load from the commercial AC power source.
Patent Document 2 also shows a construction that an output of a DC generator such as a fuel cell is connected to an DC output of a bidirectional DC-AC power inverter, to which connection a DC outlet is coupled through a DC power conversion device. AC system power and an AC load are coupled to an AC terminal of the bidirectional DC-AC power inverter.
Moreover, Patent Document 3 includes a DC power inverter for inverting DC voltage generated by a fuel cell generator, and an AC-DC power converter for converting AC power to DC power. A DC load and a DC output terminal of the AC-DC power converter are connected to an output terminal of the DC power inverter, and AC system power and an AC load are connected to an AC input terminal of the AC-DC power converter.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-254694
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2003-204682
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2007-124830